飞机能够在空中水平飞行的原因是（）

     The children often play soccer in the garden(花园). Sometimes they break (打破).Mrs. Smith’s windows.  
One afternoon , Mrs. Smith is reading a newspaper at home. After a short time, she closes her eyes and goes to sleep. At that time a little boy knocks(敲) at the door. Mrs. Smith opens the door and asks, “Do you break my windows again（又一次）?” “Oh, no”, says the boy. “ Your windows are open this time and our soccer is in your room. Can I get it back, please?” 
根据短文内容，选择正确答案。

1951年，法国、联邦德国等六国组建了“欧洲煤钢联营”。1958年，又组建了“欧洲经济共同体”和“欧洲原子能共同体”。1967年，这三个组织合并，成立了“欧洲共同体”。1993年，正式结成欧洲联盟。1999年，欧元正式启用。这段材料主要叙述了（　　）